Polarizers used in polarizing plates are optical devices enabling natural light or optionally selected polarized light to be converted into polarized light having specific directionality and have been widely used in display devices such as liquid crystal display devices and organic light emitting devices (OLED). As polarizers used in display devices to date, polyvinyl alcohol (PVA)-based polarizing films including an iodine-based compound or dichroic dye and having a molecular chain aligned in a predetermined direction have generally been used.
Polyvinyl alcohol-based polarizing films have commonly been manufactured through a method of dying polyvinyl alcohol-based films with iodine or a dichroic dye to then be oriented and crosslinked in a predetermined direction. In this case, such an orientation process may be performed through a wet orientation process performed using a solution such as a boric acid aqueous solution or an iodine aqueous solution or through a dry orientation process performed in an atmospheric environment, where an orientation magnification is generally five or more times. However, in order to perform an orientation process in the manufacturing process according to the related art without the occurrence of breakage, polyvinyl alcohol-based films are required to have a thickness greater than 60 μm before the orientation process is performed. When polyvinyl alcohol-based films have a thickness of 60 μm or less before the orientation process, a degree of swelling of polyvinyl alcohol-based films may be increased, and a modulus of elasticity per unit area may be increased due to a relatively reduced thickness such that breakages may easily occur in an orientation process.
On the other hand, in accordance with the recent trend for slimness in display devices, polarizing plates are also required to have a relatively reduced thickness. However, when polyvinyl alcohol-based films having a thickness exceeding 60 μm before an orientation process as in the case of the related art are used, there may be limitations in reducing polarizer thicknesses. Therefore, research into the manufacturing of polarizers having a relatively reduced thickness has been undertaken.
Korean Patent Laid-Open Publication No. 2010-0071998 discloses a method of manufacturing a thin film polarizing plate using a stacked body manufactured by coating a base layer with a hydrophilic polymer layer (a PVA resin layer) or co-extruding a base layer formation material and a hydrophilic polymer layer formation material (a PVA resin). However, in the case of the coating method or the coextrusion method in which a PVA layer is coated or co-extruded on a base layer, since a polyvinyl alcohol layer may not be easily separated from the base layer after the orientation process is performed and relatively great peel strength is required for the separation thereof, a problem in which the polyvinyl alcohol layer is damaged or transformed during the separation process, or the like, may occur. As a result, physical optical properties such as a degree of polarization of manufactured polyvinyl alcohol polarizers, or the like, may be degraded. In addition, when the coating method or the coextrusion method is used, since thin film polarizers are manufactured in a scheme of dissolving a polyvinyl alcohol resin and then extruding the same or producing a coating solution and applying the same, physical properties of polyvinyl alcohol films manufactured according to extrusion conditions, coating conditions, or unveiling conditions may be easily changed. Thus, difficulties in implementing uniform physical properties are present while physical properties of consequently manufactured polyvinyl alcohol films are deteriorated.